The invention is in the field of metal clad laminates used to manufacture printed wiring boards. More particularly, the invention relates to a process for fabricating laminates to desired dimensions from a block of laminates.
In its simplest form, a printed wiring board laminate includes, as a component, a dielectric layer of either a reinforced or non reinforced resin that is known in the art as a prepreg. On the opposite sides of the prepreg are bonded conductive metal foil sheets. Subsequently, after curing, the metal on the laminate, through a number of photolithographic processes, is etched to produce conductive paths, or circuits, on the surface of the cured dielectric layer. This layer may be used individually as a two sided printed wiring board, or assembled with other etched layers to produce a multilayer printed wiring board.
These laminates are typically assembled by alternately stacking conductive metal foil sheets, prepreg sheets and separator sheets into a press xe2x80x9cbookxe2x80x9d. The book is then inserted into a lamination press where it is cured under heat and pressure into a printed wiring board laminate. After pressing, the cured, metal-clad laminates are typically detached from the separator sheets and are subjected to further processing.
Of extreme importance in the manufacture of these laminates is the requirement for preventing and eliminating, to the greatest possible extent, contamination of the metallic foil sheets and maintaining cleanliness during the manufacturing process. It is known that the main cause of contamination is the presence of resin dust, fiberglass various other types of foreign material resulting from earlier manufacture and cutting of the laminates. During the manufacturing process, great care is taken to prevent resin dust and other contaminants from settling on the metallic surfaces.
It is of additional importance in the manufacture of laminates for printed wiring boards to increase the quantity of laminates produced while reducing the costs associated with materials and labor.
Laminates can be produced with metallic or composite separator sheets which inhibit laminates from adhering to each other and imparting their surface finish to the laminate. Generally, books of laminate containing separator sheets are separated or broken down prior to being cut into panels of desired sizes and dimensions. The laminates are generally pressed between thick metallic plates to maintain flatness and to assure the application of even pressure. The metallic plates represent a significant capital investment. Typically, 8-30 laminates are pressed in a book inserted into each opening within a multi opening press. Laminates may also be formed using a thin, sacrificial separator sheet. After pressing, the laminates are sent to a breakdown system, which may be manual or automatic, during which the metallic plates and/or separator sheets are removed. Following breakdown, the laminates either proceed directly to or are stacked prior to an automated or manual fabrication system to be cut one at a time.
The process of breaking down the books prior to cutting makes the laminates vulnerable to handling damage, contamination and staining as discussed hereinabove. Handling laminates in full sheet size also magnifies the chances of damage from bending or edge impacts during cutting. Additionally, handling the laminates in full sheet size requires additional process steps which decreases quantity output and overall productivity.
It is obvious from the foregoing that the elimination of handling damage and contamination incurred during the breakdown of the books, as well as increasing the quantity and quality output of laminates, in addition to reducing labor and costs of production by simplifying the process, is extremely important with regard to the manufacture of laminates used in the manufacture of printed wiring boards.
The present invention offers productivity and quality advantages associated with the production of laminates used in the manufacture of printed wiring boards. More particularly, the present invention is directed to a process for producing laminates in good quantity and with a significant decrease in imperfections. As used herein, the term xe2x80x9claminatexe2x80x9d refers to a single metal-dielectric-metal layered sheet that has been bonded together in a press during which the cure reaction of the resin is completed. The process according to the present invention is generally directed to cutting stacks comprising a plurality of laminates separated from one another by a separator component, generally in the form of separator sheets, without removing the separator sheets upon the transfer of the laminate stack from the press to the cutting apparatus. In this manner, the laminates are pressed with the separator sheets intact and the separator sheets will be sacrificial. By cutting an entire book comprised of numerous stacks with the separator sheets intact, the chances for damaging the surface of the laminate or the chances of introducing handling damage are significantly reduced. Cutting the book of laminates with the separator sheets retained therein significantly reduces the time and labor required to break down the separator sheet from the laminates as was required in prior art laminate cutting processes. Furthermore, cutting the books, or partial, or multiple books, with the separator sheet intact stabilizes the laminate during cutting. The stabilization of the laminate results in very high edge quality on the panels, which allows for the introduction into a clean room environment without secondary cleaning.
The process of the present invention provides for the buildup of a laminate which may comprise a plurality of copper-clad laminates separated by sheets of aluminum, steel, composite or other materials, which may be attached to the separator sheet using for example, CAC(trademark) (copper/aluminum/copper, which is described in U.S. Pat. No. 5,153,050), or other joining methods or positioned freely between the laminates. CAC(trademark) is commercially available from Gould Electronics Inc., Foil Divisision, Eastlake, Ohio The book of laminates is then placed in a curing press and pressed into a cured block. Without breaking down the cured block of laminates and removing the separator components, the book is transferred to a cutting apparatus, such as a paneling saw or router, which is capable of fabricating multiple laminates simultaneously. One or more books, or partial books, can be fabricated at the same time. Finally, the laminates are sized to predetermined consumer-selected dimensions.